Quadraphonic sound

Operation

Quadraphonic audio reproduction on vinyl records was problematic, because some systems were based on discrete sound channels (allowing for full separation of the four original recorded channels, albeit with restricted high-frequency response and reduced record life), while others were matrix encoded into two tracks that would also play back in standard, two-channel, stereo on normal audio equipment (so-called "compatible" quadraphonic). Also, there were inexpensive "derived" solutions that only provided back ambience channels, not a defined placement of individual instruments.

Quadraphonic systems based on tape were also introduced, based on new equipment capable of playing four discrete channels.

A full, four-channel (Quadraphonic) system will reproduce the Left Front, Left Back, Right Front, and Right Back audio signals in each of four separate speakers. Regardless of discrete or matrix formats, in four-channel stereo the rear speakers should be of the same or almost-same size or quality and have the same or almost-same frequency range as the front speakers.

Discrete (4-4-4) formats

Discrete reproduction is the only true Quadraphonic system. As its name suggests, with discrete formats the original four audio channels are passed through a four-channel transmission medium and presented to a four-channel reproduction system and fed to four speakers. This is defined as a 4–4–4 system.

Matrix (4-2-4) formats

With Matrix formats, the four channels are converted (encoded) down to two channels. These are then passed through a two-channel transmission medium (usually an LP record) before being decoded back to four channels and presented to four speakers. To transmit 4 individual audio signals in a stereo-compatible manner, there must be four simultaneous linear equations to reproduce the original 4 audio signals at the output. The term "compatible" indicates that:

1. A single-channel (mono) system will reproduce all four audio signals in its one speaker.
2. A two-channel (stereo) system will reproduce the Left Front & Left Back audio signals in the Left speaker and the Right Front & Right Back signals in the Right Speaker.

The original systems (DY & EV-4) were basic and suffered from low front L/R separation (around 12db) and a poor rear L/R separation of 2db. The decoders were designed more to give an effect rather than accurate decoding, which was mainly due to limitations in both systems, although as both systems were very closely related mathematically, users only needed one decoder of either system to play back albums of both systems.

The poor decode performance was the main reason for their disappearance once the improved matrix systems arrived based on the work by Peter Scheiber. His basic formula utilized 90-degree phase-shift circuitry to enable enhanced 4-2-4 matrix systems to be developed, of which the two main leaders were Columbia's SQ and Sansui's QS Systems.

The differences between the original systems and the new were so large that it made it impossible to decode DY/EV-4 with either SQ or QS decoders with any accuracy, the results being just a form of artificial quad.

This 4:2:4 process could not be accomplished without some information loss. That is to say, the four channels produced at the final stage were not truly identical to those with which the process had begun.

Derived (2-2-4) formats

Derived (2-2-4) formats were inexpensive electronic solutions that provided back ambiance channels from regular stereo records. There was not a deliberate placement of individual instruments on the back channels.

Quadraphonic open reel tape (Q4)

The first medium for 4-channel sound was reel-to-reel tape, used first in European electronic-music studios by 1954, an outstanding example of which was the tape part of Karlheinz Stockhausen’s piece, Kontakte (1958–60), and was introduced to the American market by the Vanguard Recording Society in June 1969 as "Quadraphonic open reel tape (Q4)" tapes. All available 4 tracks were used in one direction on the tape, running at twice the speed of the regular 4-Track reel-to-reel tapes.

Quadraphonic 8-Track Tape (Q8)

RCA Records followed, in April 1970, with its announcement of a 4 channel version of the 8-track tape, named Quad-8 or Quadraphonic 8-Track Tape (later shortened to just Q8). These eventually appeared in Sept. 1970. There were automobile players as well as home versions.

The format was almost identical in appearance to stereo 8-tracks, except for a small sensing notch in the upper left corner of the cartridge. This signaled a quadraphonic 8-track player to combine the odd tracks as audio channels for Program 1, and the even tracks as channels for Program 2. The format was not backward-compatible with stereo or mono players; although quadraphonic players would play stereo 8-tracks, playing quadraphonic tapes on stereo players resulted in hearing only one-half the channels at a time.

The last release in the quadraphonic 8-track format was in 1978, although most had stopped appearing by the end of 1976.

Matrix vinyl formats

Quadraphonic records did not remain restricted to the discrete-channel format used in reel-to-reel or 8-track tapes. Quadraphonic vinyl albums appeared, using several different and incompatible recording modes.

EV-4/Stereo-4 and Dynaco (DY)

The first of these were basic systems with poor performance developed by Electro-Voice (EV-4/Stereo-4) and Dynaco (Dynaquad (DY)). A so-called matrix format, it utilized four sound channels which were "encoded" into two stereo album tracks. These were then "decoded" back into the original four sound channels, but with poor decode performance that failed to match the discrete formats.

QS Regular Matrix and SQ Quadraphonic

Improved systems based on Peter Scheiber's work on utilizing 90-degree phase-shift circuitry came later, namely the QS and SQ systems.

The first of these, known as QS, was developed by Sansui Electric. A so-called matrix format, it utilized four sound channels, which were "encoded" into two stereo album tracks. These were then "decoded" back into the original four sound channels. The QS system debuted in the United States in March 1971 and be improved by Vario-Matrix system in 1973.

The second, SQ, was developed and marketed by Columbia Records and Sony and entered the US market in April 1971. The SQ format was also used by companies such as EMI in Great Britain, who pressed several SQ album releases. The sound separation of the SQ system was greatly improved by the introduction of SQ Full Logic decoding in 1975 using the Motorola chips MC1312, MC1314 & MC1315.

CD-4 or Quadradisc

The third major format for 4-channel vinyl LPs, known as CD-4 or Quadradisc, was devised by the Japanese JVC Corporation along with its United States counterpart RCA.

This quadraphonic format was first marketed in the United States in May 1972. A fully discrete sound mode, it eschewed the previous matrix systems in favor of a more complex method of 4-channel reproduction.

UD-4 / UMX / BMX

UD-4/UMX was developed by Nippon/Columbia (Denon). This is a hybrid discrete/matrix system. Only 35 to 40 items are encoded in this format and it was marketed only in the UK, Europe, and Japan.

The system suffered from incompatibility with regular stereo playback due to phase differences between the left and right channels.

UD-4 was less critical in its setup than CD-4 because the carriers did not have to carry frequencies as high as those found in the CD-4 system.

Radio broadcast formats

There were some experiments done with radio broadcasts (e.g., a Cliff Richard concert by the BBC, whose earliest quadraphonic broadcast was in July 1974), but they were short-lived.

One radio series, Double Exposure, was briefly syndicated throughout the United States to various FM stations; it was made up of jazz, rock and pop music that had been commercially released in one of the quadraphonic record or tape systems.

One of the longest-lived radio broadcasts was WQSR-FM "Quad 102½" in Sarasota, Florida. Throughout most of the 1970s this station broadcast a signal which could be tuned as two separate stations with conventional stereo receivers.

In addition, San Francisco classical music station KKHI broadcast the San Francisco Opera in "compatible" (that is, matrix-encoded) quadraphonic format during the 1970s, as did Chicago station WFMT's live "Chicago Lyric Opera" broadcasts..

KRMH-FM ("Good Karma Radio")(San Marcos/Austin, Texas) broadcast in "Quad Stereo" in the early 1970s from its studios and transmitter near Buda, Texas.

KEXL-FM ("KEXL 104.5") (San Antonio, Texas) broadcast in "Quadraphonic" in the early to mid 1970s from its studios in a high-rise office building off Main Plaza.

Sacramento station KWOD 106.5, named after the format, broadcast briefly beginning in 1977.

Matrix H

Matrix H was developed by BBC engineers to carry quadraphonic sound via FM radio in a way that would be most compatible with existing mono and stereo receivers.

Quadraphonic test programmes were made for BBC Radio 3 and BBC Radio 4, including plays and The Proms.

The existing matrix formats were tested first. The "H" has no meaning; they called the first matrix assessed Matrix A, and then worked through the alphabet. Matrix H emerged as the best solution for mono compatibility and radio transmission, yet there was no specific commercially available decoder for it.

The BBC later cooperated with the developers of Ambisonics to produce BBC/NRDC System HJ. This was based on tolerance zones designed to include modified versions of both Matrix H and the prototype two-channel encoding of Ambisonics, known as System 45J. Subsequently, the Nippon-Columbia UMX matrix was brought into the standard, leading to the final UHJ name now associated with Ambisonics.

Universal SQ

In 1976, Ben Bauer integrated matrix and discrete systems into USQ, or Universal SQ (others had done this with their quad systems too).

It was a hierarchical 4-4-4 discrete matrix that used the SQ matrix as the baseband for discrete quadraphonic FM broadcasts using additional difference signals called "T" and "Q". For a USQ FM broadcast, the additional "T" modulation was placed at 38 kHz in quadrature to the standard stereo difference signal and the "Q" modulation was placed on a carrier at 76 kHz.

For standard 2-channel SQ Matrix broadcasts, CBS recommended that an optional pilot-tone be placed at 19 kHz in quadrature to the regular pilot-tone to indicate SQ encoded signals and activate the listener's Logic decoder. CBS argued that the SQ system should be selected as the standard for quadraphonic FM because, in FCC listening tests of the various four channel broadcast proposals, the 4:2:4 SQ system, decoded with a CBS Paramatrix decoder, outperformed 4:3:4 (without logic) as well as all other 4:2:4 (with logic) systems tested, approaching the performance of a discrete master tape within a very slight margin. At the same time, the SQ "fold" to stereo and mono was preferred to the stereo and mono "fold" of 4:4:4, 4:3:4 and all other 4:2:4 encoding systems.

Live concerts

In 1967 the rock group Pink Floyd performed the first-ever surround-sound rock concert at “Games for May”, a lavish affair at London’s Queen Elizabeth Hall, where the band debuted its custom-made quadraphonic speaker system. The control device they had made, the Azimuth Co-ordinator, is now displayed at London's Victoria and Albert Museum, as part of their Theatre Collections gallery.

Current situation

The rise of home theatre products in the late 1980s and early 1990s brought multi-channel audio recording back into popularity, although in new digitally based formats. Some of the 1970s quadraphonic recordings have been reissued in modern surround sound formats such as DTS, Dolby Digital, DVD-Audio and Super Audio CD.